My Avant just failed its French Controle Technique (CT - equivalent to the UK MOT Test), because of an oil leak.

The amount of oil lost is insignificant, but it pools on the lower engine cover and spreads all over the underside when driving.

Running the engine while stationary with the lower cover removed results in about one small drop per minute, which drips from the flange at the bottom of the block immediately below the oil filter housing, onto/into the main cross member, and eventually down from there.

It is definitely not coming from the turbo oil feed connector, which is clean and dry, which leaves the oil filter gasket, the oil cooler O-ring, and the oil filter bracket to engine block gasket as possible suspects.

There is also a very small steering oil leak from one of its cooler connections, which is obvious.

I plan to start tomorrow by putting the lock carrier in the service position, necessary to access the steering oil cooler connections, and drain most of the coolant.
This will enable me to remove the oil filter and cooler, check the gasket and O-ring, and check tighten the mounting bolts for the filter housing.

I have ordered a new filter housing gasket as a precaution, and have a spare oil filter, and a cooler with new O-ring in stock for my VW camper, which is the same as the Audi one, but don't want to use these unnecessarily.

I'm wondering if someone distorted the oil cooler sealing surface in the past by over tightening the filter, and if this is a possibility.

Has anyone here had a similar small leak, and what was the cause, please?